In the present proposal, functional and immunocytochemical techniques will be applied to a detailed analysis of early events during lesion formation in multiple sclerosis (MS), particularly as they pertain to receptor or adhesion molecule-related lymphocyte-endothelial cell interactions and to the possible enhancing effect of intercurrent infections. For this, receptors for high endothelial venules (HEV) and presence of various adhesion molecules such as leukocyte function associated antigens (LFA-1, LFA-2, LFA-3), Class II major histocompatibility (MHC) antigen (HLA-DR: Ia) and receptors for the third complement component (CR3) will be demonstrated in frozen sections of central nervous system (CNS) tissue an on circulating lymphocytes from MS and controls by monocolonal antibodies (mAb) in combination with immunocytochemical techniques. Adherence of lymphocytes to frozen sections of MS and control CNS tissue and the blocking effect of specific antibodies will also be investigated. To study in more detail involvement of glial elements in lesion pathogenesis, Class I and Class II MHC antigens and interleukins will be demonstrated on astrocytes and oligodendrocytes characterized in double-labelling studies by antibodies to glial fibrillary acidic-protein (GFAP) and 2'-3'-cyclic nucleotide 3'-phosphohydrolase (CNP). A possible effect of intercurrent infections on microglia proliferation will be evaluated. Furthermore, labelling patterns of microglia and macrophages for various immunologic markers such as MHC antigens, receptors, immunoglobulins (Ig), enzymes and tumor necrosis factor (TNF) will be compared, to investigate possible differences in markers between these two cell types. For a more detailed analysis of T cell subsets according to their immunologic function, new mAb will be applied in combination with CD4 and CD8. This will allow to dissect helper/inducer (CD4+4B4+) T cells from suppressor/inducer (CD4+ 2H4+) T cells and suppressor (CD8+ CD11+) T cells from cytotoxic (CD11-) T cells. With the help of mAb (B-1, B-2, B-4, PCA-1), B cells at various stages of differentiation will be demonstrated. These studies might provide new information on interactions between immune cells and glial elements and might elucidate some of the mechanisms involved in lesion formation in MS. Cultured human astrocytes and oligodendrocytes will be employed to study lymphokine-induced MHC expression and involvement in antigen presentation.